You can do it on each wiki by changing the user permissions for the groups or for all (which is group '*'). ($wgRevokePermissions['*']['spamblacklistlog'] = true;)
You want this changed as default? Than it should be mention in the summary.
Maybe you want this on a specifiy wmf wiki or all wmf wikis? Than this should be a site request (or changing the default in the extension).
I agree that this log should be visible to everyone on wmf wikis. There is no harm in having this visible to everyone, so the default in the extension should be changed.
I don't see a harm, but at the same time I don't think we want wikis to be hosting lists of spam urls, so this is fine for a WMF config switch if someone wants to do that, but I don't think we should change the default.
Nope, I just changed my mind I guess (and had totally forgotten about this ticket). I think initially this ticket was about all users (*), while my patch just made it visible by logged-in users (user). But I think that should be good enough to resolve this task.